The inches gained during long stays in space don’t stick around once the adventurers return to Earth

Once humans reach their adult height, there’s very little anyone can do to make them taller. There is incredibly painful bone lengthening surgery—but it's rather extreme. Unlike planet-bound Earthlings, however, astronauts can gain several inches during long stays in space. But recent research shows there's a catch: As soon as they return to Earth they not only lose that height boost, but the whole process can lead to back problems, reports Hanna Devlin for The Guardian.

Researchers examined six NASA astronauts, each of whom spent between four and seven months on the International Space Station. Before liftoff, each astronaut had an MRI scan of their spine. Upon their return they were scanned two more times, once immediately following their arrival on Earth and again two months later, according to a press release.

The scans showed that while in space, the lean muscle mass supporting their spines atrophied, decreasing by an average of 19 percent. During follow-up scans, the astronauts had only recovered about two-thirds of their preflight muscle mass. The decrease put the astronauts at four times the risk for spinal disc herniation compared to control subjects. The astronauts also “grew” an average of about two inches because of "spinal unloading." But that height soon disappeared as they readjusted to the weight of their bodies back on Earth. The research appears in the journal Spine.

About 70 percent of astronauts report spine discomfort after only a few days in space, writes Devlin, and half experience back pain on their return to Earth. It was thought that the pain was caused by the swelling of spinal discs when the weight of the body was lifted, but the MRI scans show no evidence of such swelling. Lead author of the study Douglas Chang of the University of California, San Diego, says they will need to conduct more research to figure out exactly what is going on.

Lewis Dartnell, an astrobiologist at the University of Westminster tells Devlin that this new research highlights one of the weak links in plans to visit Mars: the human body. Having slipped discs or extreme back pain when arriving at the Red Planet after two years in space could prove deadly.

“The Moon is like a long weekend’s holiday. You’re fine to take photos of your footprints and plant some flags,” he said. “When you get to Mars there’s a serious chance you might fall off the ladder when you climb out of the spacecraft. It might be much more serious than a bit of a gripe and a joke. If you break your hip on Mars, you’re basically dead.”

In the press release, Chang says astronauts may be able to counter some of the changes through core-strengthening exercises and workout regimens suggested for people with back pain on Earth. Yoga could also be useful to help reduce problems. But more tests are needed to figure out which exercises (or if any at all) could help protect astronaut spines—or if entirely different protective measures are needed.

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About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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